It’s good to have some handy references on JavaScript programming while working on Ajax-related projects:
JavaScript, the Definitive Guide, Fifth Edition by David Flanagan (O’Reilly Media, 2006)
Pro JavaScript Techniques by John Resig (Apress, 2006)
Learning JavaScript by Shelley Powers (O’Reilly Media, 2007)
I’m particularly fond of Peter-Paul Koch’s web site, which has tons of useful resources:
He has all the example scripts from his book (http://www.quirksmode.org/book/) that you can study at
http://www.quirksmode.org/book/examplescripts.html.